The invention relates generally to barrels for directing the path of a dischargeable projectile, such as a firearm barrel or artillery barrel, and methods for forming same. More particularly, the invention relates to a composite gun barrel comprising a fiber reinforced polymer matrix composite incorporating longitudinal stiffening rods.
One attribute associated with high-performance in a gun barrel is stiffness. Higher stiffness increases the resonant frequency of the barrel and suppresses the amplitude of waves generated when a projectile, e.g. a bullet, travels down the bore, resulting in less muzzle displacement when the bullet exits and greater accuracy. Increased stiffness also reduces muzzle depression or droop when a weight, such as a suppressor, is attached to the barrel, resulting in reduced point of impact shift of the projectile. All else equal, a stiffer barrel is generally better for any caliber weapon, from small arms to large bore military cannons. Barrels intended for precision shooting conventionally achieve greater stiffness by increasing the diameter and mass of the barrel compared to barrels used for general purpose shooting/hunting. In many applications, however, less barrel mass is desired.
It is known to substitute relatively strong but lightweight materials—such as unreinforced and reinforced polymers, continuous glass fiber or carbon fiber composites—for various portions of the gun commonly fabricated from steel, aluminum, or other metals. Attention has focused on gun barrels, which constitute a large percentage of a gun's weight. It is known, for example, to fabricate a gun barrel having a steel inner liner surrounded by a carbon fiber reinforced polymer matrix composite (PMC) outer shell, incorporating a resin. This combination lightens the gun while retaining good barrel strength and stiffness.
The carbon fibers used in the PMC outer shell may be any type that provides the desired stiffness, strength and thermal conductivity. Typically for PMC gun barrel applications, polyacrylonitrile (“PAN”) precursor or pitch precursor carbon fibers are used. The carbon fiber may be applied as dry carbon fiber strands or tows which are combined with a resin in a “wet” dip pan process, then wound around the inner liner. Alternatively, the shell may be built from carbon fiber tow, unidirectional tape, or fabric that was previously impregnated with resin in a separate process (“towpreg” or “prepreg”), then applied to the inner liner. Whether applied wet or dry, the matrix resin is typically an epoxy but may also be a polyimide or any other suitable resin. The composite barrel may then be cured, finished, and attached to a receiver with a trigger mechanism and a stock to produce a firearm.
Composite firearm barrels in the prior art are often significantly lighter than conventional steel barrels, but may not exhibit comparable stiffness. In some cases it is possible to manufacture a composite barrel with light weight and good stiffness, but at a higher cost or sacrifice to other performance attributes. What is needed is a composite barrel having improved stiffness.